Environmental Drivers of Soil Microbial Diversity and Metabolic Potential Across the Western Himalayan Treeline

Although soil microbial communities in high-altitude environments are a vital component of ecosystem functioning, their structural and functional responses to elevation and environmental heterogeneity are poorly known. This study explored the composition, diversity, and functional potential of the soil microbial community along elevation in the western Himalayan ecotone, using high-throughput metagenome sequencing. Physicochemical profiling based on 13 parameters revealed pronounced spatial variability among soil samples. A total of 4,394 species were identified, with a resilient core microbiome comprising 1,772 shared species across all samples. The bacterial genera Azorhizobium , Buchnera , Shewanella , and Dictyoglomus were found to be dominant, indicating key roles in nitrogen fixation, metal cycling, and cellulose degradation. Functional annotation identified 193 MetaCyc pathways and over 149,000 gene families, with significant variation in pathway richness and composition along elevation. Vegetation transition zones showed the highest functional diversity and unique pathway presence. Core metabolic pathways such as nucleotide biosynthesis, folate metabolism, and fatty acid synthesis were highly enriched across sites. Stress-related pathways were found to be more pronounced as elevation increases. Redundancy analysis revealed iron, moisture content, and electrical conductivity as major environmental drivers of both microbial composition and functional traits. These findings emphasise the ecological importance of environmental gradients in shaping microbial communities and their functions, offering critical insights into microbial adaptation and ecosystem processes in mountain treeline environments.